1. Field of the Invention
The present invention relates to an automated workpiece handling system for a machine tool and, more particularly, to a method and apparatus for transporting workpieces to, feeding workpieces onto, conveying workpieces along, feeding workpieces off of, and transporting workpieces from a machine tool.
2. Description of the Prior Art
Automated machinery is often used to perform a variety of operations on a workpiece, such as drilling and/or routing. A modern automated machine tool typically includes a plurality of workstations spaced along a movable worktable, with each of the workstations having an alignment device and a drilling and/or routing mechanism. The alignment device aligns and secures a workpiece, such as a group of printed circuit boards, to the worktable so that the drilling and/or routing operation can take place.
Previously, the workpieces have been inserted onto the alignment device of the individual workstations by hand. The machine tool then performs a programmed series of operations on the workpieces and the workpieces are manually removed upon completion of these operations. Thus, a typical automated machine tool requires the constant attention of a human operator.
The manual insertion and removal of workpieces from an automated machine tool is tedious work and can result in inefficient operation of the machine. Human labor is relatively expensive and should therefore be used for tasks which can best utilize the talents that a human operator has to offer. Furthermore, the manual handling of the workpieces can adversely affect the output efficiency of the machine because of the speed of the operator.
For some time, it has been recognized that a highly practical machine tool should have a fast, efficient system for bringing the workpieces to the workstations and for removing the workpieces after the operations are completed. It has been further recognized that such a system should operate in a relatively economical manner and should preferably not require any human labor. One attempt to provide an automated handling system for a machine tool is described in U.S. patent application Ser. No. 236,884, filed Feb. 23, 1981 now Pat. No. 4,364,320, entitled Handling System for an Automated Tooling Machine and assigned to the same assignee as the present invention. Such handling system incorporates a transporter which carries the workpieces to the workstation of an automated tooling machine. The transporter incorporates a mechanism for feeding the workpieces onto the worktable at a selected workstation. The machine tool then incorporates a mechanism for carrying the workpieces from station to station.
The system is relatively complex and since the loading mechanism is part of the transport means, the loading mechanism must be duplicated for each transport means and the transport means is complex and expensive. The conveyor belt system for moving the workpieces from station to station is also complex. An improved system is disclosed in application Ser. No. 470,457, filed Feb. 28, 1983, also assigned to the same assignee as the present invention. That application discloses an automated workpiece handling system in which the loading and unloading mechanism is part of the machine tool so that it need not be duplicated. Furthermore, the mechanism for moving the workpieces along the machine tool partially uses the worktable itself so that the system for conveying the workpieces from station to station is also simple. This system includes rails which may be elevated with respect to the worktable and wiper blades which extend into the path of the workpieces when the rails are elevated. In order to shift workpieces along the worktable the rails are initially lowered and the table shifted to an extreme position. The rails are then raised and the worktable shifted to the opposite extreme position. The wiper blades prevent the workpieces from moving with the worktable. The rails are then again lowered and the worktable is shifted back to the first extreme position. In this fashion, the workpieces are shifted from workstation to workstation along the worktable.
A drawback of the above system is that the handling mechanism is open loop in that it does not provide any positive feedback regarding the position of the workpiece. That is, it is assumed that the workpiece is being properly transported to the various workstations. However, the workpieces are unconstrained from lateral and rotational movements, resulting in inconsistent positioning of workpieces.